Dicing semiconductor wafers is known to introduce cracks that can propagate across chips and lead to chip failure. As shown in FIGS. 1a and 1b, semiconductor wafer 10 is diced into individual chips 12 with high speed circular metallic or resin saw blade 14 having embedded diamond particles 16 while wafer 10 is rinsed with water 18. The impact of high speed particles of diamond or silicon and the lateral motion of saw blade 14 within the dicing channel--known as saw blade chatter and shown in FIG. 1b--frequently damage chip edges 20. The damage may be a crack initiated in semiconductor substrate 22. It may also be a delamination at the interface between the semiconductor substrate 22 and an overlying insulator or between any of the overlying metal layers and insulating layers.
Once delamination crack 30 in overlying film 32 is initiated, it can propagate inward from edge 20 across the surface of chip 12 to active regions of the chip, as shown in FIG. 2. Particle and blade impacts during dicing can combine with thermal or deposition stresses inherent in thin film layers on a semiconductor to drive delamination cracks into the active device area of the chip. In addition, metals and other thin film layer materials, such as oxide and nitride insulators, can react with aqueous dicing fluid 18 or atmospheric moisture to provide a stress-corrosion mechanism for delamination advance. Thus, delamination cracks tend to propagate across the chip, and these cracks can cause electrical opens or shorts and, ultimately cause failure of the semiconductor chip.
To improve chip yield and reliability, several methods have been proposed to either prevent initiation of delamination cracks or to reduce the probability of delamination crack propagation, as shown in FIGS. 3a-3d. For example, all of the layers may be removed from dicing channel 40 before dicing, as shown in FIG. 3a. Thus, dicing blade initiation of delamination cracks between any of the six thin film metallization layers shown and adjacent insulation layers is avoided. In addition, after removal of all thin film layers in dicing channel 40, ductile or shock absorbing material 42 can be used to prevent particles generated during dicing from contacting or interfering with nearby brittle thin film layers, as shown in FIG. 3b. Alternatively, small trenches 44 can be etched into one or more of the top layers on either side of dicing channel 40' to stop propagation of cracks in those layers, as shown in FIG. 3c. Of course, cracks initiated in lower lying layers D0-D6 will not be stopped by small trenches 44 of FIG. 3c. By contrast, deep trenches 46 of FIG. 3d can be used to prevent propagation of delamination cracks initiated in dicing channel 40' in any layer of the structure.
Unfortunately, introducing a gap such as gap 40, 44, or 46 adds additional process steps and substantial cost. This is particularly the case where active device areas must be masked during the etching steps required to form a gap or where different materials are +layered, and different etchants must be used sequentially for removal of the layers. Furthermore, any deposition steps for ductile material 42 adds yet additional costs, and adding ductile material in the dicing channel leads to excessive dicing blade sticking and poor dicing quality. Thus, a solution is needed that more effectively suppresses crack propagation without adding processing steps or cost, and this solution is provided by the following invention.